1. Field of the Invention
The present invention relates to a method for determining at least one rail pressure/closing current value pair for a pressure control valve of a common rail injection system.
2. Description of the Related Art
Common rail systems (CRS) for fuel injection are widely used at the present time in diesel engines. Modern common rail systems are frequently equipped with a so-called dual-actuator rail pressure regulator. In such a system, the injection pressure is set either by throttling the high-pressure pump via a valve (metering unit (MU)) situated upstream from the pump, or via a valve (pressure control valve (PCV)) situated on the high pressure side. Thus, in principle, the rail pressure may be regulated in such a system via three different operating modes (MU, PCV, and mixed operation). This is used in particular for diesel vehicles, for example on the one hand to introduce heat into the fuel system immediately after a cold start during cold weather (PCV operation with high power loss) and thus to minimize the risk of paraffination, and on the other hand to minimize the power loss during warm-weather operation by compressing only the fuel mass that is actually needed (MU mode). Switching between the two types of control modes requires accurate knowledge of the characteristic curves of both valves so that overshooting or undershooting of the pressure may be minimized. Namely, in particular for the pressure control valve, the closing current is a function of the prevailing rail pressure. In the following discussion, “characteristic curve” is understood as a number of rail pressure/closing current value pairs, i.e., the associated closing current of the valve at a given prevailing rail pressure.
The PCV characteristic curve is preferably adapted using a functionality known as the adaptive pressure control valve (APCV). For this purpose, in PCV mode when (quasi)-steady-state operating conditions are present, the actual current necessary for setting the desired rail pressure is measured, and is compared to an expected setpoint current. The ratio of the two currents is then stored as a learning value or adaptation value. To achieve high accuracy in the adaptation, this learning process should be applied at the highest possible operating pressures.
However, in many cases these required operating pressures are reached only at very high engine loads. In addition, due to environmental considerations, operation strictly in PCV mode should be avoided to the greatest extent possible. As a result of both of these factors, APCV adaptation occurs only infrequently. Furthermore, regulatory standards in many countries require more frequent determination of a PCV characteristic curve, i.e., one or multiple rail pressure/closing current value pairs.
It is therefore desirable to provide an adaptation method for a pressure control valve, having an increased learning frequency.